com.googlecode.javaewah.BitCounter Maven / Gradle / Ivy

Go to download

Show more of this group Show more artifacts with this name
Show all versions of JavaEWAH Show documentation

The bit array data structure is implemented in Java as the BitSet class. Unfortunately, this fails to scale without compression. JavaEWAH is a word-aligned compressed variant of the Java bitset class. It uses a 64-bit run-length encoding (RLE) compression scheme. The goal of word-aligned compression is not to achieve the best compression, but rather to improve query processing time. Hence, we try to save CPU cycles, maybe at the expense of storage. However, the EWAH scheme we implemented is always more efficient storage-wise than an uncompressed bitmap (implemented in Java as the BitSet class). Unlike some alternatives, javaewah does not rely on a patented scheme.

There is a newer version: 1.2.3

Show newest version

package com.googlecode.javaewah;
/*
 * Copyright 2009-2016, Daniel Lemire, Cliff Moon, David McIntosh, Robert Becho, Google Inc., Veronika Zenz, Owen Kaser, Gregory Ssi-Yan-Kai, Rory Graves
 * Licensed under the Apache License, Version 2.0.
 */

/**
 * BitCounter is a fake bitset data structure. Instead of storing the actual
 * data, it only records the number of set bits.
 *
 * @author David McIntosh
 * @since 0.4.0
 */

public final class BitCounter implements BitmapStorage {

    /**
     * Virtually add words directly to the bitmap
     *
     * @param newData the word
     */
    @Override
    public void addWord(final long newData) {
        this.oneBits += Long.bitCount(newData);
    }
    
    /**
     * Virtually add literal words directly to the bitmap
     *
     * @param newData the word
     */
    @Override
    public void addLiteralWord(final long newData) {
        this.oneBits += Long.bitCount(newData);
    }

    /**
     * virtually add several literal words.
     *
     * @param buffer the buffer wrapping the literal words
     * @param start  the starting point in the array
     * @param number the number of literal words to add
     */
    @Override
    public void addStreamOfLiteralWords(final Buffer buffer, int start, int number) {
        for (int i = start; i < start + number; i++) {
            addLiteralWord(buffer.getWord(i));
        }
    }

    /**
     * virtually add many zeroes or ones.
     *
     * @param v      zeros or ones
     * @param number how many to words add
     */
    @Override
    public void addStreamOfEmptyWords(boolean v, long number) {
        if (v) {
            this.oneBits += number * EWAHCompressedBitmap.WORD_IN_BITS;
        }
    }

    /**
     * virtually add several negated literal words.
     *
     * @param buffer the buffer wrapping the literal words
     * @param start  the starting point in the array
     * @param number the number of literal words to add
     */
    @Override
    public void addStreamOfNegatedLiteralWords(final Buffer buffer, int start, int number) {
        for (int i = start; i < start + number; i++) {
            addLiteralWord(~buffer.getWord(i));
        }
    }

    @Override
    public void clear() {
        this.oneBits = 0;
    }

    /**
     * As you act on this class, it records the number of set (true) bits.
     *
     * @return number of set bits
     */
    public int getCount() {
        return this.oneBits;
    }

    /**
     * should directly set the sizeInBits field, but is effectively ignored
     * in this class.
     *
     * @param bits number of bits
     */
    // @Override : causes problems with Java 1.5
    @Override
    public void setSizeInBitsWithinLastWord(int bits) {
        // no action
    }

    private int oneBits;
}